The invention relates to a process for operating a vehicle fuel tank system, in particular a cryo tank system, for example, for liquid hydrogen, whereby elements of the tank system, like lines, valves or the like and/or a storage container for the fuel, are enveloped at least partially by a capsule, the interior of which is vented at least from time to time. Furthermore, the invention relates to a corresponding vehicle fuel tank system. For the technical environment reference is made to the DE 195 46 618 C2 and also to the EP 0 069 717 B1 solely for the sake of providing an example.
Searching for alternative drive energies for motor vehicles, one is also working with liquefied gases in general and with hydrogen in particular. In this respect a liquefied gas or hydrogen in the liquid form is stored in a so-called cryo tank. Different lines, in which there are, for example, valves, but also heat exchangers or generally fluid conveying elements of the tank system, lead into the tank or out of the tank, thus, among other things, to the fuel operated internal combustion engine. Another line, leading out of a cryo tank, can serve to carry away the so-called boil off gas.
In cryo tank systems it is customary to encapsulate at least sections or parts of these aforementioned or also other system elements, that is to arrange inside a so-called capsule that is built around these elements or parts of the same. Optionally this capsule can also enshroud the vehicle tank itself. This capsule, which, with the exception of an optionally blockable venting line, is sealed against its immediate environment for various reasons, can extend simply from the actual tank up to the internal combustion engine or the like, to be supplied with the fuel, stored in the tank.
Moreover, the use of such a capsule in a vehicle tank system is not limited to a cryo tank system. Rather an encapsulation can also be realized in past conventional motor vehicle tank systems, in which gasoline or diesel fuel is stored, in order to meet the increasingly tighter legal regulations regarding the evaporation losses from the fuel system. In addition, a capsule of an LNG tank system can also be appropriate.
Basically gas concentrations that are critical under unfavorable conditions can form in the said capsule. Due to leakage, which is not always totally avoidable, gaseous fuel can flow from the fuel tank system into the interior of the capsule and collect there. Furthermore, when in the case of a cryo tank its gases are exhausted in a line through the capsule, there is the risk that the air will be liquefied in this extremely cold exhaust line, the result of which is an oxygen enrichment in the capsule. Thus, the formation of ignitable mixtures in the capsule cannot be ruled out with absolute certainty, and in particular not even if this capsule is vented. Such venting occurs at least in the in-house state of the art using a venting line, emptying outside the vehicle, whereby the capsule serves primarily to collect leakage gases of the tank system and to prevent these gases from penetrating into the interior of the vehicle.
Furthermore, the simple exhausting of gases, collecting in the capsule, into the environment is not always nonproblematical, if it occurs at all on a sufficient scale. In addition to possible environmental problems, one can name in this connection fundamental problems relating to the approval process for the vehicle due to legal regulations.
Therefore, the object of the present invention is to provide a measure to remedy the described problems.
With respect to the operating process for a vehicle fuel tank system, the solution to this problem is characterized in that to vent the interior of the capsule, a pressure difference is produced and that the gas, which is exhausted thus and which flows over unavoidable leakages from the tank system into the interior, is further processed and thus specifically disposed so that there is no danger to the environment.
With respect to the related claim, relating to a vehicle fuel tank system, the solution to the said problem is characterized in that, in addition to a device for generating a pressure differential between the interior of the capsule and the environment in a connecting line to the environment, there is a disposal device for the exhausted gas, which flows over unavoidable leakages out of the tank system into the interior of the capsule, in which this gas is further treated in such a manner that there is no danger to the environment.
Additional embodiments are discussed further below.